Qingdao's government said the pipeline — owned by China's largest oil refiner, Sinopec — leaked for about 15 minutes before it was shut off, spilling onto a street and contaminating more than 3,000 square meters (32,000 square feet) of sea surface. The explosions happened hours later as workers cleaned up the spill.

"We will investigate the incident with responsibility and give timely reports," Sinopec said in a statement.

"It felt like an earthquake, and I was dumbstruck," said Gao, a resident of Qingdao who was driving past the district where the explosions occurred when he felt the blasts and saw the ground in front of him fracture.

Friday's incident is likely to worsen growing concerns among the Chinese public regarding safety and environmental risks related to oil pipeline projects.

The explosions were China's third deadliest industrial accident this year, after a chicken factory fire in June that killed 121 and a mining accident in March that left 36 dead.